Dump path light intensity sensing in light projector

ABSTRACT

In a light projection system, potentially hierarchical levels of light intensity control ensure proper laser-light output intensity, color channel intensity, white point, left/right image intensity balancing, or combinations thereof. The light projection system can include a light intensity sensor in an image path, in a light-source subsystem light-dump path, in a light-modulation subsystem light-dump path, in a position to measure light leaked from optical components, or combinations thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed concurrently with and has related subjectmatter to:

U.S. patent application Ser. No. ______, titled “Stereoscopic ImageIntensity Balancing in Light Projector”, with Barry Silverstein as thefirst named inventor and an attorney docket number of 95598;

U.S. patent application Ser. No. ______, titled “Hierarchical LightIntensity Control in Light Projector”, with Barry Silverstein as thefirst named inventor and an attorney docket number of 95599;

U.S. patent application Ser. No. ______, titled “Image Path LightIntensity Sensing in Light Projector”, with Barry Silverstein as thefirst named inventor and an attorney docket number of 95600; and

U.S. patent application Ser. No. ______, titled “Leakage Light IntensitySensing in Light Projector”, with Barry Silverstein as the first namedinventor and an attorney docket number of 95602,

each of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention generally relates to monitoring and control of lightintensity in a light projection system.

BACKGROUND OF THE INVENTION

There is growing interest in high-quality projection systems thatdisplay three-dimensional (3D) or perceived stereoscopic content inorder to offer consumers an enhanced visual experience in large venues.Although a number of entertainment companies have offered stereoscopiccontent in theaters, theme parks, and other venues, these companies haveprimarily employed film media for stereoscopic image presentation. Tocreate the stereo image, two sets of films are loaded to two separateprojection apparatus, one for each eye. Left- and right-eye images arethen simultaneously projected using polarized light. One polarization isused for the image presented to the left eye; light of the orthogonalpolarization is then used for the image presented to the right eye.Audience members wear corresponding orthogonally polarized glasses thatblock one polarized light image for each eye while transmitting theorthogonal polarized light image.

In the ongoing transition of the motion picture industry to digitalimaging, some vendors, such as Imax, have continued to utilize atwo-projection system to provide a high quality stereo image. Morecommonly, however, conventional projectors have been modified to enable3D projection.

The most promising of these conventional projection solutions formulticolor digital cinema projection employ, as image forming devices,one of two basic types of spatial light modulators (SLMs). The firsttype of spatial light modulator is the Digital Light Processor (DLP) adigital micromirror device (DMD), developed by Texas Instruments, Inc.,Dallas, Tex. DLPs have been successfully employed in digital projectionsystems. DLP devices are described in a number of patents, for exampleU.S. Pat. No. 4,441,791; No. 5,535,047; No. 5,600,383 (all to Hornbeck).

The second type of spatial light modulator used for digital projectionis the LCD (Liquid Crystal Device). The LCD forms an image as an arrayof pixels by selectively modulating the polarization state of incidentlight for each corresponding pixel. LCDs appear to have some advantagesas spatial light modulators for high-quality digital cinema projectionsystems. These advantages include relatively large device size,favorable device yields and the ability to fabricate higher resolutiondevices, for example 4096×2160 resolution devices available from Sonyand JVC Corporations. Among examples of electronic projection apparatusthat utilize LCD spatial light modulators are those disclosed in U.S.Pat. No. 5,808,795 (Shimomura et al.) and elsewhere. LCOS (LiquidCrystal On Silicon) devices appear particularly promising forlarge-scale image projection. However, with LCD components it can bedifficult to maintain the high quality demands of digital cinema,particularly with regard to color and contrast, since the high thermalload of high brightness projection affects polarization qualities ofthese devices.

Conventional methods for forming stereoscopic images from theseconventional micro-display (DLP or LCOS) based projectors use either oftwo primary techniques to distinguish between the left and right eyecontent. One less common technique, utilized by Dolby Laboratories, forexample, uses color space separation, as described in US PatentApplication Publication No. 2007/0127121 by Maximus et.al. andelsewhere. Filters are utilized in the white light illumination systemto momentarily block out portions of each of the primary colors for aportion of the frame time. For example, for the left eye, the lowerwavelength spectrum of Red, Blue, and Green (RGB) is blocked for aperiod of time. This alternates with blocking the higher wavelengthspectrum of Red, Blue, and Green (RGB) for the other eye. Theappropriate color adjusted stereo content that is associated with eacheye is then presented to each modulator for the eye. The viewer wears acorresponding filter that similarly transmits only one of the two3-color (RGB) spectral sets.

The second method for forming separate stereoscopic images usespolarized light. In the example embodiment of U.S. Pat. No. 6,793,341 toSvardal et al. and elsewhere, each of two orthogonal polarization statesis delivered to a corresponding one of two separate spatial lightmodulators. Polarized light from both modulators is then projectedsimultaneously. The viewer wears polarized glasses with polarizationtransmission axes for left and right eyes orthogonally oriented withrespect to each other.

Another approach, commercialized by Real-D, Beverly Hills, Calif., usesa conventional projector modified to modulate alternate polarizationstates that are rapidly switched from one to the other. This can bedone, for example, where a DLP projector has a polarizer placed in theoutput path of the light. The polarizer is required, since the DLP isnot inherently designed to maintain the polarization of the input light,which is generally unpolarized, as the window of the device packagedepolarizes due to stress induced birefringence. An achromaticpolarization switcher, similar to the type described in US application2006/0291053 by Robinson et al. could be disposed after the polarizer. Aswitcher of this type alternately rotates polarized light between twoorthogonal polarization states, such as linear polarization states, toallow the presentation of two distinct images, one to each eye, whilethe user views with polarized glasses.

Regardless of whether stereoscopic or monoscopic images are formed,digital projection systems have recently incorporated solid-state lightsources, particularly LEDs and lasers, and arrays of these sources.These solid-state light sources offer a number of advantages overearlier lamp-based illumination sources used for color projection. Amongsuch advantages are component life, spectral characteristics,brightness, and overall efficiency. For example, when compared againstarc lamp and other solutions using a single white light source,solid-state sources expand the available color gamut for projection.

One problem raised by the use of solid-state light sources relates toachieving a suitable balance of the light output from each colorchannel. Driver circuitry for solid-state light sources can befactory-calibrated to obtain a target white point or color balance froma projector. However, factors such as component aging and drift candegrade the initial color adjustment so that the color balance is nolonger acceptable. This problem is even more pronounced for stereoscopicimaging. An image formed for the left eye of the viewer should closelymatch the corresponding image formed for the right eye of the viewer interms of overall brightness and color balance. Failure to achieve acompatible intensity of color channels for left- and right-eye imagescan render the projected stereoscopic images as unappealing or, atworst, as visually disturbing to the viewer.

Thus, there is a need to provide a greater measure of control over lightintensity output by light projection systems, for monoscopic as well asfor stereoscopic projection.

SUMMARY OF THE INVENTION

The above-described problem is addressed and a technical solution isachieved in the art by systems and methods for monitoring or controllinglight intensity, according to various embodiments of the presentinvention. In an embodiment of the present invention, a light projectionsystem includes an image forming subsystem and a projection subsystem.The image forming subsystem can include a plurality of light modulationchannels. Each light modulation channel can include a light sourcesubsystem that generates coherent light of a particular color channel.The generated light can travel along an image path to a light modulationsubsystem configured at least to interact with the coherent light in amanner consistent with image data. Depending upon the image data, thelight modulation subsystem passes light it receives to the projectionsubsystem for projection or along a dump path to a beam dump.

The light projection system can include a light-intensity-correctionsubsystem. The light-intensity correction subsystem can include a lightintensity sensor in the image path, in the dump path, or in a positionthat receives light leaked from an optical component in the imageforming subsystem. In embodiments where the image forming subsystemgenerates stereoscopic light, such image sensor can be located in alight dump path associated with the light source subsystem (to becontrasted with the light dump path associated with the light modulationsubsystem). The light-intensity-correction subsystem can be configuredto monitor and control light intensity output by individual lasers inthe light source subsystem, color channel light intensity for each lightmodulation channel, left-eye/right-eye light beam balancing, whitepoint, or combinations thereof.

In embodiments where combinations thereof are monitored and controlled,the light-intensity-correction subsystem can further be configured tobalance white point, color channel intensities, or both, by reducing theintensity output by one or more color channels when another colorchannel cannot have its output increased. Such an arrangement allowswhite point and color channel intensity to remain balanced even whenlasers experience lower intensity output with age or failure.

It is an advantage of the present invention that it allows automaticfine-tuning adjustment of output intensity on multiple levels: laser,color channel, left/right stereoscopic, and white point, to compensatefor drift and component aging or failure.

These and other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there is shown and described an illustrativeembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood from the detaileddescription of exemplary embodiments presented below considered inconjunction with the attached drawings, of which:

FIG. 1 illustrates optical components in a light projection system thatcan be common to various embodiments of the present invention;

FIG. 2 illustrates a monoscopic light source subsystem with alaser-light intensity control subsystem, according to some embodimentsof the present invention;

FIGS. 3-5 illustrate a light source subsystem with a laser-lightintensity control subsystem, the light source subsystem capable ofgenerating stereoscopic and monoscopic light, according to someembodiments of the present invention;

FIG. 6 illustrates a color channel intensity control subsystem with alight-intensity sensing subsystem located, at least in part, in an imagepath, according to some embodiments of the present invention;

FIG. 7 illustrates a method for monitoring and controlling color channelintensity, according to some embodiments of the present invention;

FIG. 8 illustrates a method for monitoring and controlling intensitybalance between left-eye and right-eye light beams, according to somestereoscopic embodiments of the present invention;

FIGS. 9 and 10 illustrate a color channel intensity control subsystemwith a light-intensity sensing subsystem located, at least in part, in aposition to measure light leaked from an optical component, according tosome embodiments of the present invention;

FIG. 11 illustrates a color channel intensity control subsystem with alight-intensity sensing subsystem located, at least in part, in a lightdump path associated with a light modulation subsystem, according tosome embodiments of the present invention;

FIGS. 12 and 13 illustrate a color channel intensity control subsystemand a white point control subsystem with a light-intensity sensingsubsystem located, at least in part, in an image path on a shutter,according to some embodiments of the present invention;

FIG. 14 illustrates a method for monitoring and controlling white point,according to some embodiments of the present invention;

FIG. 15 illustrates a white point control subsystem with alight-intensity sensing subsystem located, at least in part, in an imagepath on a shutter, according to some embodiments of the presentinvention;

FIG. 16 illustrates a hierarchy of individual laser, color channel, andwhite point control loops, according to some embodiments of the presentinvention;

FIG. 17 illustrates a hardware implementation of a laser light intensitycontrol subsystem, according to some embodiments of the presentinvention;

FIG. 18 illustrates a hardware implementation of a color channelintensity control subsystem, according to some embodiments of thepresent invention;

FIG. 19 illustrates a hardware implementation of a white point controlsubsystem, according to some embodiments of the present invention;

FIG. 20 illustrates relative sampling frequencies associated with ahierarchy of individual laser, color channel, and white point controlloops, according to some embodiments of the present invention; and

FIG. 21 illustrates one particular circuit layout that can be used toimplement a particular embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present description is directed in particular to elements formingpart of, or cooperating more directly with, apparatus in accordance withthe invention. It is to be understood that elements not specificallyshown or described may take various forms well known to those skilled inthe art.

Figures shown and described herein are provided to illustrate principlesof operation according to the present invention and are not drawn withintent to show actual size or scale. Because of the relative dimensionsof the component parts for the laser array of the present invention,some exaggeration is necessary in order to emphasize basic structure,shape, and principles of operation.

The invention is inclusive of combinations of the embodiments describedherein. References to “a particular embodiment” and the like refer tofeatures that are present in at least one embodiment of the invention.Separate references to “an embodiment” or “particular embodiments” orthe like do not necessarily refer to the same embodiment or embodiments;however, such embodiments are not mutually exclusive, unless soindicated or as are readily apparent to one of skill in the art. The useof singular and/or plural in referring to the “method” or “methods” andthe like is not limiting.

It should be noted that, unless otherwise explicitly noted or requiredby context, the word “or” is used in this disclosure in a non-exclusivesense.

Embodiments of the present invention address the need for improvedmonitoring and control of light intensity in coherent-light projectionsystems. For example, embodiments of the present invention provideimproved intensity balancing between left-eye and right-eye images instereoscopic projection systems. For another example, embodiments of thepresent invention provide various light-intensity sensor configurationsallowing a preferred configuration to be chosen based on design choice.For yet another example, embodiments of the present invention provideimproved system-level intensity control with a feedback system. Thefeedback system manages white-point intensity control via feedback froma color-channel intensity control system, and manages color-intensitycontrol via feedback from a laser-intensity-control system. For stillyet another example, embodiments of the present invention includefailure response procedures that adjust light intensity in manners thataccount for the inability of one or more light sources to achieve athreshold light output intensity. These and other capabilities andbenefits will be described in more detail in the remainder of thisdescription.

In order to better understand the various embodiments of the presentinvention, it is instructive to first describe example components thatcan be common to such various embodiments. These example components areshown in FIG. 1, which illustrates a light projection system 10 that canbe used for embodiments of the present invention. However, one ofordinary skill in the art will appreciate that the invention is notlimited to the particular optical components and configuration thereofshown in FIG. 1 and that other optical components, configurations, orboth can be used.

The light projection system 10 includes an image forming system 11 (alsoreferred to as an image forming subsystem) that outputs light 15.Depending upon whether the image forming subsystem 11 is configured tobe a monoscopic or stereoscopic image forming system using techniquesknown in the art, the light 15 can be monoscopic or stereoscopic.Consequently, the light projection system 10 can be a monoscopic or astereoscopic light projection system 10, depending upon theconfiguration of the image forming subsystem 11.

The light 15 output from the image forming subsystem 11 is received by aprojection system 13 (also referred to as a projection subsystem) thatprojects a monoscopic or stereoscopic image, depending upon theconfiguration of the image forming subsystem 11. In this regard, theprojection subsystem 13 can include one or more lens elements as isknown in the art. In some embodiments, the projection subsystem 13projects the monoscopic or stereoscopic image towards a display surface80.

The light 15 can include multiple color channels of light. In FIG. 1,the light 15 includes red, green, and blue modulated color channels oflight from light modulation channels 40 r, 40 g, and 40 b, respectively.However, one of ordinary skill in the art will appreciate that theinvention is not limited to any particular number or configuration ofcolor channels. In FIG. 1, the red, green, and blue color channels arecombined by a dichroic combiner 17 to form the light 15 output from theimage forming system 11.

In the example of FIG. 1, each light modulation channel 40 r, 40 g, and40 b includes a coherent light source system 42 (also referred to as acoherent light source subsystem or just a light source subsystem). Notethat FIG. 1 includes reference numerals for the components of only thered light modulation channel 40 r for purposes of clarity. However, itshould be understood that the same components are also represented inFIG. 1 for the other light modulation channels 40 g and 40 b, albeitwithout reference numerals.

Each coherent light source subsystem 42 emits a single color channel ofthe multiple color channels of light, in this case, red, green, or blue.Consequently, each coherent light source subsystem 42 emits coherentlight 41 along an image path 21, optionally into a lens 50 that directslight into an optional polarization maintaining light guide 52. Althoughthe image path 21 is shown straight in FIG. 1, it need not be. Also,although the light guide 52 is shown as being rectangular forsimplicity, one of ordinary skill in the art will appreciate that lightguides often take different shapes, such as a tapering shape. At theoutput of light guide 52, or otherwise directly receiving light fromlens 50 or light source system 42, a lens 54 then directs light throughan integrator 51, such as a fly's eye integrator or integrating barknown in the art, for example. The light exiting the integrator 51proceeds downstream along the image path 21 to a light modulation system(or subsystem) 60. The light modulation subsystem 60 can include aspatial light modulator, known in the art.

Each light modulation subsystem 60 interacts with the light it receives(originally from corresponding light source subsystem 42) in a mannerconsistent with image data, such as image data representing an imageframe in a movie. In this regard, control signals are provided to eachlight modulation subsystem 60 by a data processing system (not shown),such as a control system, that controls each light modulator subsystem60 in the manner consistent with image data using techniques andequipment known in the art. In particular, the light modulationsubsystems 60 can include two-dimensional arrays of addressablemodulator pixels (not shown) that modulate incident light in accordancewith the image data signals. Light modulation can be provided by avariety of devices, including redirection by tilting of micro-mirrors(DLP), polarization rotation (LCOS or LCD), light scattering,absorption, or diffraction.

Each light modulation subsystem 60 causes light generated from therespective light source subsystem 42 to follow either the image path 21or a respective light dump path 19 in a manner consistent with the imagedata. The light dump path 19 leads to a respective beam dump 22 and doesnot lead to the projection subsystem 13. On the other hand, the imagepath 21 does lead to the projection subsystem 13. For example, if theimage data indicates that a particular pixel is to be fully bright,i.e., have maximum intensity, the respective light modulation subsystem60 causes the light associated with such pixel to fully pass along theimage path 21. On the other hand, if the image data indicates that aparticular pixel is to be fully off, i.e., have no light intensity, therespective light modulation subsystem 60 causes the light associatedwith such pixel to fully pass along the light dump path 19. In the casewhere the image data indicates that a particular pixel is to havemoderate intensity, i.e., not fully on or fully off, the respectivelight modulation subsystem 60 causes some of the light associated withsuch pixel to pass along the image path 21 and some to pass along thelight dump path 19. Although FIG. 1 shows a separate light dump path 19and beam dump 22 for each light modulation channel, some or all of thelight modulation channels 40 can share a light dump path 19 and beamdump 22, depending upon design choice.

Light passed or directed along the image path 21 by the light modulationsubsystem 60 gets combined with corresponding light from the other lightmodulation channels 40 g, 40 b by dichroic combiner 17. The combinedlight 15 output by dichroic combiner 17 (and, consequently, the imageforming subsystem 11 in this example) passes through an optional shutter65 (when it is in an open position) and onto the projection subsystem13. In certain situations, the shutter 65 can be in a closed position,such as when the light projection system 10 is warming up or is in alight-intensity measurement or other diagnostic state. When the shutter65 is in a closed position, further projection of downstream-progressinglight, whether monoscopic or stereoscopic, is prevented. In other words,no light exits the image forming subsystem 11 or, consequently, thelight projection system 10. The shutter 65 is moved into its open andclosed positions by a motor 66 and additional mechanical components (notshown) that are known in the art.

The projection subsystem 13 directs the modulated light output from theimage forming subsystem 11 to a display surface 80. As discussed above,the light projection subsystem 13 can project monoscopic images,stereoscopic images, or both, depending upon design of the image formingsubsystem 11. Although the invention is not limited to any particularconfiguration of the image forming subsystem 11 to generate eithermonoscopic or stereoscopic light, FIGS. 2 illustrates just one exampleof a light source subsystem 42 that generates monoscopic light, andFIGS. 3-5 illustrate just one example of a light source subsystem 42that generates stereoscopic light.

In FIG. 2, monoscopic light is generated from a plurality of individuallasers 26 (not all are labeled with a reference numeral in FIG. 2 forpurposes of clarity). In this example, the individual lasers 26 areformed in solid state laser arrays 44, which are driven by laser drivers94, 94′. It should be noted that laser drivers 94, 94′ are merely shownsymbolically in FIG. 2 and need not be integrally formed with laserarrays 44, as shown. Laser drivers are well known in the art, and theinvention is not limited to any particular configuration. Similarcomments pertain to FIG. 3, described below. Coherent light emitted fromthe laser arrays 44′ are redirected by mirrors 46 so that they arecombined with the coherent light emitted from the laser array 44. Thelaser-light intensity measurement system 49 shown in FIG. 2 (and FIGS. 3and 4) will be described below.

In FIG. 3, stereoscopic light is generated from two banks of polarizedsolid state laser arrays 44 a, 44 b (not all are labeled with areference numeral in FIG. 3 for purposes of clarity). Polarized laserarrays 44 a and 44 b, driven by laser drivers 94 a, 94 b, provide lightto respective light redirecting prisms 31, known in the art. The lightredirecting prisms 31 redirect the light they receive towards a rotatingshutter 71. A half-wave plate 64 converts light from laser arrays 44 ainto a polarization state orthogonal to the light from laser arrays 44b. The light output by the half-wave plate 64 represents a right-eyelight beam 58, which has an orthogonal polarization state to theleft-eye light beam 57.

A rotating shutter 71 is located in the path of the optical axis mergedbetween the orthogonal polarization states. The position of the rotatingshutter 71 is controlled by control circuitry 74 that controls a motor72. Rotating shutter 71, shown in FIG. 4, has a transmissive disk with aleast two segments. A first segment 71 a is designed to substantiallytransmit all of the light that is incident upon it. The alternatesegment 71 b is designed to substantially reflect all of the light thatis incident upon it. When transmission segment 71 a lies along theoptical axis, laser arrays 44 b transmit through to the rest of theimage forming subsystem 11, while laser arrays 44 a are transmittedalong a light dump path 76 to be absorbed by a beam dump 73. The lightsource subsystem light dump path 76 is to be contrasted with the lightmodulation subsystem light dump path 19, in some embodiments. Inparticular, the light dump path 76 is associated with a light sourcesubsystem 42 for some stereoscopic embodiments, and dumps the left-eyelight beam or right-eye light beam, whichever one is in an off state perFIG. 5. On the other hand, the light dump path 19, in some embodiments,is associated with a light modulation subsystem 60, and dumps light(whether monoscopic or stereoscopic) that is not needed to form an imageper image data.

Optional individual laser light-intensity sensors 93 are describedlater. Alternately, when reflective segment 71 b (FIG. 4) is along theoptical axis, light from laser arrays 44 a (FIG. 3) are reflectedthrough to the rest of the image forming subsystem 11, and light fromlaser arrays 44 b is directed to beam dump 73. In this manner, outputlight 41 (FIG. 1, FIG. 3) of alternating orthogonal polarizations isdelivered along the image path 21 to the spatial light modulationsubsystem 60, as shown in FIG. 1. The spatial light modulation subsystem60 generates stereoscopic images from this light 41 in a mannerconsistent with left-eye and right-eye image data.

It should be noted that a transition region 71 c exists betweenpolarization states, as shown in FIG. 4. Light 75 between the tworegions 71 a and 71 b contains both polarization states. This conditioncauses crosstalk between the images of the two eyes, also known asghosting. Some amount of crosstalk may be acceptable. If the crosstalkis excessive, the spatial light modulation subsystem 60 may be turned tothe off state during this transition period, eliminating the crosstalkat the cost of some lost light. The time when the spatial lightmodulation subsystem 60 is off between left-eye and right-eye light beamgeneration is referred to as a blanking period. Therefore, it can bedesirable to reduce the transition region 71 c. Such reduction can beachieved by either reducing the spot size of the light 75 or byenlarging the shutter wheel 71, placing the light 75 as far toward theouter diameter as practical.

For non-stereoscopic applications of the embodiment of FIG. 3, the lightfrom both banks of polarized laser arrays 44 a and 44 b may be usedtogether to provide a brighter monoscopic image (regardless ofalternating polarizations). The laser arrays 44 a, 44 b can be used athalf power to balance the lifetime of each laser source and to generatea monoscopic image as bright as the stereoscopic image. In this regard,it can be seen that the light source subsystems 42 can generate bothmonoscopic and stereoscopic images in a single configuration.

Returning to FIG. 2, a light-intensity-correction subsystem 23 isillustrated that includes a laser-light intensity control subsystem 49(sometimes referred to as “L1” or “L1 subsystem”) in a monoscopic lightsource subsystem 42, according to an embodiment of the presentinvention. One skilled in the art will appreciate, however, that thesubsystem 49 can be used with other monoscopic implementations besidesthe one shown in FIG. 2. The laser-light intensity control system 49monitors and controls output light intensity from each laser 26. Inembodiments where the laser-light intensity control system 49, or thelaser-light-intensity control system 23, for that matter, includes onlya monitoring function, such systems are sometimes referred to herein as“measuring” systems instead of “control” systems.

Monitoring of output light intensity from each laser 26 can occur in anynumber of ways. For example, monitoring of light-intensity of a laser 26can occur within the corresponding laser array 44, using techniquesknown in the art. In this case, a feedback loop, not shown, wouldconnect each laser array 44 to the L1 subsystem 49. Another techniquefor monitoring light intensity of an individual laser is to place alight intensity sensor, such as a photo-diode, in a position to receiveand measure light originating from a laser, but leaked from an opticalcomponent in the image forming subsystem. For example, a photo-diodecould be placed behind a mirror (such as one of the mirrors 46) or othersubstantially reflective optical element that reflects such laser lightbeam. Typically, the best mirror coatings will still leak around 0.2 to0.5% of the light incident. Such leakage light can be measured todetermine intensity of the corresponding laser light beam. In thisregard, a photo-diode (not shown) could be placed behind one of themirrors 46 at a position that would measure leaked light from orsubstantially from a laser beam from one of the lasers 26. Suchtechniques can also be used to measure color channel intensity and whitepoint described below.

According to some embodiments of the present invention, the L1 subsystem49 controls output light intensity from each laser 26 either byincreasing or decreasing voltage or current to or adjusting duty cycle(repeated on/off time) of laser drivers 94, 94′ associated with eachlaser array 44, 44′. Such drivers 94, known in the art, have associatedcircuitry, not shown, that allows output light intensity control of eachindividual laser 26 in associated laser array 44, 44′.

FIGS. 3 and 4 illustrate a light-intensity-correction subsystem 23 thatincludes a laser-light intensity control subsystem 49 in a stereoscopiclight source subsystem 42, according to an embodiment of the presentinvention. One skilled in the art will appreciate, however, that thesubsystem 49 can be used with other stereoscopic implementations besidesthe one shown in FIGS. 3 and 4.

As with the monoscopic embodiment of FIG. 2, the laser-light intensitycontrol system 49 monitors and controls output light intensity from eachlaser 26. In this regard, although any technique can be used, outputlight intensity from each laser 26 can be measured internally by thecorresponding laser arrays 44 a, 44 b. Another example is to measureoutput light intensity from each laser 26 using corresponding individuallaser light-intensity sensors 93 on beam dump 73. In this case, as lightfrom either laser arrays 44 a or 44 b are passed to the beam dump by therotating shutter 71, individual laser light-intensities can be measured.Accordingly, feedback from sensors 93 can be provided to the L1subsystem 49 by some communicative connection, not shown in FIG. 3. Alsoas with the embodiment of FIG. 2, the laser-light intensity controlsystem 49 monitors and controls output light intensity from each laser26.

FIGS. 6-13 illustrate color-channel-level intensity monitoring andcontrol according to various embodiments of the present invention. Inparticular, FIG. 6 illustrates a light-intensity-correction subsystem 23for the red light modulation channel 40 r, according to an embodiment ofthe present invention. The light-intensity-correction subsystem 23 shownin FIG. 6 can be repeated for each of the other color channels. In someembodiments, the light-intensity-correction subsystem 23 includes acolor channel intensity control subsystem 47 (sometimes referred to as“L2” or “L2 subsystem”) and a light-intensity sensing subsystem 92. Thesensing subsystem 92 can include one or more sensors, such asphotodiodes, that measure light intensity. Thelight-intensity-correction subsystem 23 can also include appropriateconnections and control circuitry, known in the art, to directly orindirectly control laser drivers 94 (not shown in FIG. 6) to adjust thecoherent light 41 generated by the light source subsystem 42, as needed.

In FIG. 6, the sensing subsystem 92 can be located in the image path 21.In this regard, the sensing subsystem 92 can be attached to a mechanicaldevice (not shown) and motor (not shown), for example, that moves thesensing subsystem 92 into and out of the image path 21. The sensingsubsystem 92 can be moved into the image path 21, for example, when theshutter 65 is closed, so that intensity measurements can be taken. Whenviewable images are being generating by the image forming subsystem 11(shown in FIG. 1, but not FIG. 6 for clarity), e.g., when the shutter 65is open, the sensing subsystem 92 can be removed from the image path 21.

FIG. 7 illustrates a method 100 performed by the L2 subsystem 47 formonitoring and adjusting a color channel intensity, according toembodiments of the present invention. At process state 102, the L2subsystem 47 determines an intensity 103 of a color channel frominformation received from the sensing subsystem 92. In the example ofFIG. 6, the L2 subsystem 47 determines an intensity of the red colorchannel from information received from the sensing subsystem 92. Atprocess state 104, the L2 subsystem 47 compares the color channelintensity 103 to a predetermined color channel intensity 105. Thepredetermined color channel intensity 105 can be, for example, a colorchannel intensity (a) set at manufacture, (b) configured by a user viauser input, (c) determined by present use of the light projection system10 (e.g., presentation of a feature film can have an associated firstcolor channel intensity, and presentation of advertisements betweenfeature films can have an associated second color channel intensity lessthan the first), (d) dependent upon present intensities of other colorchannels, (e) controlled by a white point control subsystem 59,discussed below, or (f) combinations thereof.

At process state 106, the L2 subsystem 47 determines whether theabsolute value of the difference 107 between the color channel intensity103 and the predetermined color channel intensity 105 is greater than athreshold amount 107. Such threshold amount 107 can be very small (e.g.,much less than 1%) depending upon the requirements of the lightprojection system 10.

If the answer is deemed “no” at process state 106, normal color channelintensity is presumed and processing returns to process state 102 forcontinued monitoring. If the answer is deemed “yes” at process state106, the L2 subsystem 47 determines at process state 108 whether thecolor channel intensity 103 can be adjusted to cause the difference 107to be within the threshold amount 109. For example, if individual lasers26 in laser arrays 44 have failed or are failing, coherent light 41generated by the corresponding light source subsystem 42 may be belowthe predetermined color channel intensity 105 by an amount greater thanthe threshold amount 109. And, because of the failed or failing lasers26, the intensity of the light 41 output by the light source subsystem42 may not be able to be increased. Consequently, the L2 subsystem 47can determine, at process state 108 that the color channel intensity 103cannot be increased to cause the difference 107 to be within thethreshold amount 109. As described in more detail below, thedetermination at process state 108 can be based, at least in part, fromfeedback provided by the L1 subsystem 49. However, the L1 subsystem 49and L2 subsystem 47 need not coexist, and some embodiments of thepresent invention have an L1 subsystem 49 without an L2 subsystem 47,and vice versa. The same applies for the white point control subsystem59, described below.

In cases where a “no” is determined at process state 108, the L2subsystem 47 adjusts the color channel intensity, if possible, to anintensity that minimizes or substantially minimizes the difference 107.In this case, an error can be reported at process state 110 to a user orto another control system, such as a white point control system 59,describe below, that can take corrective action. Such corrective actioncan be to set the predetermined color channel intensity 105 for thepresent and the other color channels to a lower intensity. For example,if the red color channel intensity is less than the predetermined colorchannel intensity 105 by an amount greater than the threshold amount109, and if the L2 subsystem 47 cannot increase the red color channelintensity, the predetermined color channel intensity 105 for this and,optionally, at least one of the other channels can be reduced. Afterprocess state 110, processing returns to process state 102 for continuedmonitoring.

In cases where a “yes” is determined at process state 108, the L2subsystem 47 adjusts or instructs adjustment of the color channelintensity 103 so that the difference 107 is within the threshold amount109 at process state 112. In some embodiments, light source subsystems42 are set at manufacture to output less than (e.g., 90%) their maximumcapable output, allowing upward adjustments of output light intensity asindividual lasers 26 age or fail. After process state 112, processingreturns to process state 102 for continued monitoring.

FIG. 8 illustrates a method 200 performed by the L2 subsystem 47 formonitoring and adjusting left-eye and right-eye color channel intensity,according to embodiments of the present invention involving stereoscopicimaging. In the case of stereoscopic projection, a perceptibledifference between light intensity for left and right eyes can easilyoccur where polarization or spectral differences are used to distinguishleft-eye from right-eye images projected for the viewer. Withpolarization-separation devices, this intensity difference can resultwhether or not the same light sources are used for the image directed toeach eye. This intensity difference is caused because there is someunavoidable amount of light leakage when using polarization components.If the intensity difference is large enough, distraction or discomfortcan occur in viewers of the images.

At process state 202, the L2 subsystem 47 determines a left-eye lightbeam color channel intensity 201 and a right-eye light beam colorchannel intensity 203 from information received from the sensingsubsystem 92. In this regard, the sensing subsystem 92 or the L2subsystem 47 can have timing circuitry that informs the L2 subsystem 47which measurements correspond to the left-eye light beam or righteye-light beam.

At process state 204, the L2 subsystem 47 compares the left-eye andright-eye color channel intensities 201, 203. At process state 206, theL2 subsystem 47 determines whether the absolute value of the difference207 between the left-eye and right-eye color channel intensities 201,203 is greater than a threshold amount 209.

If the answer is deemed “no” at process state 206, a normal colorchannel intensity difference is presumed between the left-eye andright-eye light beams and processing returns to process state 202 forcontinued monitoring. If the answer is deemed “yes” at process state206, the L2 subsystem 47 determines at process state 208 whether theleft-eye color channel intensity 201 or the right-eye color channelintensity 203 can be increased to cause the difference 207 to be withinthe threshold amount 209. Consequently, it can be seen that theseembodiments at process state 208 lend a preference to increasingintensity to fix intensity differences. However, the invention is notlimited to such a preference, and decreasing intensity can be preferred.

If the light beam (left or right) with the lesser intensity cannot beincreased, a “no” is deemed correct at process state 208. In this case,the light-intensity-correction subsystem 23 controls the image formingsubsystem 11, or more specifically, the corresponding light sourcesubsystem 42 of the image forming subsystem 11, to reduce the left-eyecolor channel intensity 201 or the right-eye color channel intensity 203at process state 210, whichever had the greater intensity. After processstate 210, processing returns to process state 202 for continuedmonitoring.

If the light beam (left or right) with the lesser intensity can beincreased, a “yes” is deemed correct at process state 208. In this case,the light-intensity-correction subsystem 23 controls the image formingsubsystem 11, or more specifically, the corresponding light sourcesubsystem 42 of the image forming subsystem 11, to increase the left-eyecolor channel intensity 201 or the right-eye color channel intensity 203at process state 212, whichever had the lesser intensity. After processstate 212, processing returns to process state 202 for continuedmonitoring.

Although FIG. 8 illustrates embodiments where either the left-eye colorchannel intensity 201 or the right-eye color channel intensity 203 isincreased or decreased to reduce the difference 207, the invention isnot so limited. One of ordinary skill in the art will appreciate thatone of the color channel intensities (left or right) can be increasedand the other decreased in order to reduce the difference 207.

FIGS. 9 and 10 illustrate a light-intensity-correction subsystem 23 thatincludes a light-intensity sensing subsystem 92 having at least onelight-intensity sensor 91 located on a side 56 of the integrator 51,according to embodiments of the present invention. The side 56 runs in adirection relatively parallel to the image path 21 or the optical axisof the integrator 51. Remember that the sides of the integrator 51 cantaper toward or away from the image path 21.

In the embodiments based on FIGS. 9 and 10, the sensing subsystem 92 ispositioned to monitor the light intensity from light leaked from theintegrator 51 along the image path 21. In this regard, FIGS. 9 and 10illustrate embodiments where a light intensity sensor is in a positionto receive and measure light leaked from an optical component, in thiscase, the integrator 51, in the image forming subsystem 11. In the caseof measuring leaked light from the integrator 51, it can be desirable tomonitor light that is substantially uniform in intensity andpolarization. Accordingly, although not required, it can be preferred toplace the sensing subsystem 92 (or a sensor therein) on a portion of theintegrator 51 where light proceeding through the integrator 51 has beensubstantially uniformized, e.g., on the downstream portion of theintegrator 51.

FIG. 10 illustrates an embodiment where the integrator 51 has atranslucent cover 53 underneath a sensor 91 on the side 56. Althoughonly one sensor 91 is shown in FIG. 10, additional sensors can be used.The translucent cover 53 can be wrapped around the integrator 51 and hasa lower index of refraction than the material of which the integrator 51is made. Such an index of refraction difference allows the translucentcover 53 to improve the total internal reflection inside the integrator51 and, consequently, to improve uniformization. Surface imperfectionson the integrator 51, however, still provide some small level of leakagelight to exit the sides of the integrator 51 and pass through thetranslucent cover 53 for measurement by the sensor 91. When the lightleakage passes through the translucent cover 53, it is further diffused,providing light that is even more uniform to the sensor 91 formeasurement.

The embodiments of FIGS. 9 and 10 can operate using the procedures ofFIGS. 7 and 8, except that the color channel intensities 103, 201, 203are determined from leakage light from the integrator 51. Calibrationprocedures can be used to determine the amount of leakage light presentat the location of the sensor 9 1.

FIG. 11 illustrates a light-intensity-correction subsystem 23 thatincludes a light-intensity sensing subsystem 92 located in the lightdump path 19. Such an arrangement can be beneficial because the sensingsubsystem 92 does not interfere with the image path 21 and can insteadmeasure intensity of light that might otherwise be wasted. In theseembodiments, the procedures of FIGS. 7 and 8 can be used by the L2subsystem 47, except that the color channel intensities 103, 201, 203are determined from light entering the light dump path 19. In thisregard, the sensing subsystem 92 measures intensity during a periodwhere the spatial light modulator 60 is at a known position, e.g., at afully off position that directs all light to the light dump path 19, ata calibration position, or some other known position.

In this regard, specific intensity measurement periods can be generatedfor the light projection system 10, not only with the embodiments ofFIG. 11, but any of the embodiments of the invention. For example, suchmeasurement periods can occur (a) during or contemporaneously withcompletion of construction of the image forming system 11, (b) during orcontemporaneously with a startup procedure initiated by a powering-on orrebooting of the image forming system 11, (c) just prior to projecting avideo with the projection system 13, (d) while the shutter 65 is closed,or combinations thereof. In regard to some stereoscopic light projectionsystems 10, a portion of the blanking period between the left and righteye light beams can be utilized as an intensity measurement period.

FIGS. 12 and 13 illustrate a light-intensity-correction subsystem 23that includes a color channel intensity control subsystem 47, a whitepoint control subsystem 59 (also referred to as the “L3 subsystem”), orboth, according to some embodiments of the present invention. In theseembodiments, the light-intensity-correction subsystem 23 also includes alight-intensity sensing subsystem 92 having at least one light-intensitysensor 91 located on the shutter 65. It should be noted that the sensingsubsystem 92 is located downstream of the dichroic combiner 17 and,therefore, is in a position to measure the intensity of all of the colorchannels. This arrangement eliminates the need for separate sensingsubsystems 92 for each color channel. Consequently, individual colorchannel intensities as well as white point (all color channelssimultaneously) can be measured and controlled. Individual color channelintensities can be monitored and controlled by the color channelintensity control subsystem 47 using the processes of FIGS. 7 and 8.White point can be measured and controlled by a white point controlsubsystem (L3 subsystem) 59 using the process of FIG. 14, describedbelow.

As shown for example in FIG. 13, the shutter 65 can be placed into anopen position 68 removed from the image path 21 or into a closedposition 67 in the image path 21 by a motor 66 and mechanical arm 69.One skilled in the art, however, will appreciate that the invention isnot limited to any particular technique for moving the shutter 65 intoand out of the image path 21. When the shutter 65 is in the closedposition 67, the light-intensity sensor 91 is placed into the image path21 for measurements. Although only one sensor 91 is shown in FIG. 13,multiple sensors can be used. When the shutter 65 is in the openposition 68, the sensor 91 is out of the image path 21. A similar designto that shown in FIG. 13 can be used for embodiments based on FIG. 6.

When the shutter 65 is in the closed position, the image forming system11 (FIG. 1) is prevented from outputting light to the projectionsubsystem 13. The closing of the shutter 65 commonly is done incommercial cinema projectors to allow the projector to maintain itsoperation while other content is shown on the screen 80. In this closedposition, the processes of FIGS. 7 and 8 can be executed by the L2subsystem 47 while only one of the light source subsystems 42 r, 42 g,42 b are on at time. In particular, each light source subsystem 42 r, 42g, 42 b can be cycled on, e.g., fully on, one at a time, while the othercolor channels are off, so that each color channel's intensity can bemeasured and adjusted, as needed.

Also while the shutter 65 is in the closed position, a white-pointmonitoring and control process 300 shown in FIG. 14 can be executed bythe white point control subsystem 59. At process state 302, a whitepoint 303 is determined from an intensity measurement received by thesensing subsystem 92 when all color channels are simultaneously in anon, e.g., fully on, state. At process state 304, the white point 303 iscompared to a predetermined white point 305. The predetermined whitepoint 305 can be, for example, a white point (a) set at manufacture, (b)configured by a user via user input, (c) determined by present use ofthe light projection system 10 (e.g., presentation of a feature film canhave an associated first white point, and presentation of advertisementsbetween feature films can have an associated second white point lessthan the first), (d) present capabilities of the light source subsystems42 r, 42 g, 42 b (e.g., lasers 26 aging or failing will impact whitepoint intensity capabilities, as discussed with respect to processstates 108 and 110 in FIG. 7), or (d) combinations thereof At processstate 306, the L3 subsystem 59 determines whether the absolute value ofthe difference 307 between the white point 303 and the predeterminedwhite point 305 is greater than a threshold amount 307. If the answer isdeemed “no” at process state 306, normal white point is presumed, andprocessing returns to process state 302 for continued monitoring.Alternatively, the shutter 65 can be opened or other action taken. Ifthe answer is deemed “yes” at process state 306, the L2 subsystem 47determines at process state 308 whether the difference 307 can bereduced to within the threshold amount 309 by increasing the intensityof one or more of the color channels. For example, a problematic lightsource subsystem 42 may be generating its maximum light intensity, butgenerating less light intensity than the other color channels (asdescribed with respect to states 108 and 110 in FIG. 7, above).Consequently, the difference 307 may be greater than the thresholdamount 309. Because this problematic light source subsystem 42 alreadyis generating maximum intensity, its color channel intensity cannot beincreased to reduce the difference 307 to within the threshold amount309. In this case, a “no” is determined by the L3 subsystem 59 atprocess state 308. It can be seen that the analysis at process state 308reflects a bias to increase color channel intensity to correct whitepoint problems. One skilled in the art will appreciate, however, thatsuch a bias is not required.

If a “no” is determined at process state 308, the intensities of one ormore color channel intensities is or are reduced to bring the difference307 to within the threshold amount 309 at process state 310. Inembodiments where both an L3 subsystem 59 and an L2 subsystem 47 arepresent, the L3 subsystem 59 at process state 310 can lower thepredetermined color channel intensity 105 for one or more colorchannels, as shown in FIG. 7.

If a “yes” is determined at process state 308, one or more color channelintensities is or are increased to bring the difference 308 to withinthe threshold amount at process state 312. In embodiments where both anL3 subsystem 59 and an L2 subsystem 47 are present, the L3 subsystem 59at process state 310 can raise the predetermined color channel intensity105 for one or more color channels, as shown in FIG. 7. Upon conclusionof process state 310 or 312, processing returns to process state 302 forcontinued monitoring. Alternatively, the shutter 65 can be opened orother action taken.

FIG. 15 illustrates white point measurement and control for embodimentswhere each color channel has its own sensing subsystem 92 for colorchannel intensity control and there is not necessarily a sensordownstream of the dichroic combiner 17 for direct sensing of whitepoint. In particular, FIG. 15 represents each color channel as havingits own portion of a light intensity control subsystem 23 r, 23 g, 23 b(as is the case in FIGS. 6, 9, and 11) for color channel control (viarespective color channel intensity control subsystems 47 r, 47 g, 47 b).In addition, FIG. 15 illustrates an additional portion of the lightintensity correction subsystem 23 w that includes a white point controlsubsystem (L3 subsystem) 59 for white point control. The L3 subsystem 59executes the process of FIG. 14 and receives individual color-channelintensity measurements from each of the portions 23 r, 23 g, 23 b of thelight-intensity correction subsystem when performing process state 302.

As alluded to above, some embodiments of the present invention include ahierarchical structure among the various intensity control subsystems.In the case of FIG. 15, the L3 subsystem 59 receives information fromthe L2 subsystems 47 r, 47 g, 47 b as to their respective present outputintensity level. The L3 subsystem 59 uses this information to check forproper white balance per the procedure of FIG. 14. If an adjustmentneeds to be made to an intensity of one of the color channels, the L3subsystem 59 instructs one or more of the L2 subsystems 47 r, 47 g, 47 bto change its predetermined color channel intensity 105 accordingly. Ifan L2 subsystem 47 r, 47 g, or 47 b cannot meet its predetermined colorchannel intensity 105, the L2 subsystem can report this condition to theL3 subsystem 59. A similar hierarchical structure can exist between theL2 subsystem 47 and the L1 subsystem 49, according to some embodimentsof the present invention. In these cases, the L2 subsystem 47 caninstruct the L1 subsystem 49 to change the output intensity of itslasers 26. If the L1 subsystem 49 cannot do so, it can report such acondition to its corresponding L2 subsystem 47.

In this regard, FIG. 16 illustrates a hierarchy of control loops L1, L2,L3 in embodiments of the present invention where all three levels ofintensity control (L1-laser, L2-color channel, L3-white point) arepresent. As mentioned earlier, some embodiments of the present inventiondo not have all three levels, such as embodiments that have only onelevel (e.g., the embodiments of FIGS. 2-4 having L1 only), orembodiments that have only two levels (e.g., the embodiments of FIGS. 6,9, 11 having L1 and L2 only). As shown in FIG. 16, feedback from the L1subsystem 49 is provided to the L2 subsystem 47 for color channelintensity control, and feedback from the L2 subsystem 47 is provided tothe L3 subsystem 59 for white point control. As described separatelyearlier in this description, the L1 subsystem 49 monitors and controlsthe output intensity of each laser 26 by controlling associated laserdrivers 94. The L2 subsystem 47 receives information from the L1subsystem 49 as to the present output intensity level and outputcapabilities of the corresponding lasers. The L2 subsystem 47 uses thisinformation to check for proper color channel output intensity,left-eye/right-eye output intensity balance, or both, per the proceduresof FIGS. 7, 8, or both, respectively. If an adjustment needs to be madeto the intensity of the lasers in light source subsystem 42, the L2subsystem 47 instructs the L1 subsystem 49 to change the intensityoutput of one or more of its lasers accordingly. Some of the informationthat can be provided by the L1 subsystem 49 to the L2 subsystem 47 caninclude a binary indication of whether or not the L1 subsystem 49 isable to obtain or maintain the laser output level instructed by the L2subsystem 47, such as per the inquiries at process state 108 or 208 inFIGS. 7 and 8, respectively. Other information can include laseroperating current, laser operating voltage, laser input power, laseroutput power, laser and driver operating temperatures, elapsed laseroperating time, or combinations thereof. The prompting of information tobe provided from the L1 subsystem 49 to the L2 subsystem 47 can beinitiated by the L2 subsystem 47 when needed, by the L3 subsystem 59when needed, by user request by expiration of a predetermined timeperiod, or combinations thereof.

The interaction between the L2 subsystem 47 and the L3 subsystem 59 inFIG. 16 is as described above with respect to FIG. 15. In the event thatthe output intensity of a color channel cannot be increased, as per theinquiry at process state 308 in FIG. 14, the L2 subsystem reports thisfact to the L3 subsystem 59.

It can be seen that control loops L1, L2, L3 are interrelated in someembodiments of the present invention. Adjustments within one of thesecontrol loops impacts the status and control of the other control loopsin the hierarchy. For example, control of the red color channel outputintensity using color channel control intensity control loop L2 canaffect not only the laser intensity control loop L1 for each red laserdriver 94, but also the white point control loop L3. Thisinterrelationship allows a measure of compensation for conditions ofcomponents within the control loop. For example, poor performance of aparticular laser in a color channel can affect the current provided toother lasers in the same color channel, such as to boost power in orderto compensate for an aging component. In the same way, white pointcontrol loop L3 can compensate for a weaker color channel by reducingthe output of other color channels in order to preserve the desiredwhite point, as previously described.

FIG. 17 illustrates a simplified hardware implementation of a portion ofthe L1 subsystem 49 that controls a single laser 26, according to someembodiments of the present invention. One skilled in the art willappreciate, however, that this design can be extended to control aplurality of lasers 26. In FIG. 17, a laser diode 155 is shown asrepresenting laser 26. However, laser arrays 44 commonly use a singlelaser diode 155 to generate multiple laser beams. For purposes ofclarity, however, FIG. 17 is described as controlling a laser diode 155.

Current through the laser diode 155 is provided by a laser currentsource 152 as a function of a control signal 158. The current source 152is part of a laser driver 94 and can be a voltage controlled currentsource, a voltage controlled voltage source with direct analog currentfeedback and internal analog control loop, or a voltage controlledvoltage source with digital control provided by an internal digitalcontrol loop and indirect current feedback. The current source 152 canbe comprised of a digital to analog converter with appropriateamplifiers and circuitry to produce the current output, in whichapproach the control voltage (in control signal 158) will exist as amathematical construct delivered to the current source 152 via one ormore binary signals. The current source 152 can alternatively compriseanalog and digital circuitry to produce a current output in directresponse to the value voltage of the control signal 158.

The photo diode 156 samples the light emitted by the laser diode 155 todetermine the intensity of this light. The current through the photodiode 156 provides the input to the transimpedance (current to voltage)amplifier 153. The output of the amplifier 153 is a voltage 159 that isproportional to the power of the light (intensity) sampled by the photodiode 156. The summation device 154 provides an error voltage 160 equalto the difference between a set voltage 157 and voltage 159 output fromamplifier 153. In this regard, the set voltage 157 acts as apredetermined laser light intensity. The set voltage 157, in someembodiments, is derived from instructions received from the L2 subsystem47. If the absolute value of the error voltage 160 is greater than apredetermined threshold amount, as determined by the control and PID/PWMcomputation circuitry 151, the control signal 158 is adjusted in amanner that brings such difference to within the threshold amount. ThePID/PWM computation circuitry 151, more elaborately referred to asProportional Integral Derivative Controller/Pulse Width Modulationcomputation circuitry 151, is known in the art.

The summation device 154, the error voltage 160 and the set voltage 157can exist as discreet physical entities or as mathematical constructswithin a digital version of the control and PID/PWM computationcircuitry 151. Depending upon the embodiment being implemented, thecontrol and PID/PWM computation circuitry 151 can receive control data,such as power or intensity output control data, from the L2 subsystem 47and report status to the L2 subsystem 47 via the power control/statusbus 162. For example, the control and PID/PWM computation circuitry 151can be instructed via the power control/status bus 162 to reduce powerto lasers when lasers from another color channel are at maximum output(per process states 110 in FIG. 7 and 310 in FIG. 14). Also, the PID/PWMcomputation circuitry 151 can report to the L2 subsystem 47 a failure toreach a requested (predetermined) laser output via the powercontrol/status bus 162. In stereoscopic embodiments, the left/rightsignal 161 is provided from the upper levels in the control loophierarchy and used by the circuitry 151 to modify the control signal 158to alter the intensity of the laser 155 output in synchronization withthe left and right image data.

FIG. 18 illustrates a hardware implementation of the L2 subsystem 47,according to some embodiments of the present invention. The control andPID/PWM computation circuitry 171 for the color channel intensitycontrol subsystem (L2) 47 monitors and controls the behavior of anentire array 172 of the lasers of a single color shown within thelaser-intensity control subsystem 49 in FIG. 18. In these embodiments,the computation circuitry 171 acts as a single communications channelbetween each of the laser control loops 150 through which command datais passed to the laser control loops 150 and status data is passed fromthe laser control loops 150.

In some of the embodiments based on FIG. 18, a light intensity sensor91, such as a photo diode, measures the color channel intensity outputby the array of lasers 172. The light intensity sensor 91 can have thelocation represented by light-intensity sensing subsystem 92 shown inFIG. 6, FIG. 9, FIG. 10, FIG. 11, FIG. 12, or FIG. 13. The voltagegenerated by sensor 91 is passed to a transimpedance amplifier 180 togenerate a signal Vpower 176 representative of the present intensity ofthe color channel. Vpower 176 is passed to a summation device 173, whichcompares Vpower 176 to a set voltage 175 and generates an error voltage174. In this regard, Vpower 176 can correspond to the color channelintensity 103 in FIG. 7, the set voltage 175 can correspond to thepredetermined color channel intensity 105 in FIG. 7, and the errorvoltage 174 can correspond to the difference 107 in FIG. 7. The setvoltage 175, in some embodiments, is derived from instructions receivedfrom the L3 subsystem 59 via power control/status bus 178. If theabsolute value of the error voltage 174 is greater than a predeterminedthreshold amount (e.g., threshold amount 109 in FIG. 7), as determinedby the control and PID/PWM computation circuitry 171, one or more of thecontrol loops 150 are instructed by the computation circuitry 171 toaccordingly adjust their laser light intensities via powercontrol/status bus 162 (see, e.g., process state 112 in FIG. 7). If thelaser light intensities cannot be adjusted to reduce the error voltage174 within the predetermined threshold amount, an error report can besent to the L3 subsystem 59 via power control/status bus 178, accordingto some embodiments (see process state 110 in FIG. 7). In stereoscopicembodiments, the left/right signal 177 is used by the computationcircuitry 171 to determine whether it is currently measuring andcontrolling color channel intensity for a left-eye light beam or aright-eye light beam. In these instances, the processes of FIG. 8 can beused.

It should be noted that, although FIG. 18 shows that the color channelintensity 176 is derived from the sensor 91, some embodiments have thecolor channel intensity 176 generated from a summation of thelaser-output intensities provided to the computation circuitry 171 viapower control/status bus 162. In other words, in lieu of using aseparate sensing system 92 for color channel intensity measurement, suchas that shown in FIGS. 6, 9, 11 and 12, for example, color channelintensity can be measured from information provided by the individuallaser control loops 150 to the computation circuitry 171 via powercontrol/status bus 162.

On the other hand, the sensor 91 in FIG. 18 may be shared by the othercolor channels, such as that shown in FIGS. 12 and 13, where the sensor91 is located downstream of the dichroic combiner 17. In theseembodiments, each color channel does not have its own sensor 91, shownin FIG. 18, but instead shares a single sensor or sensing system.

FIG. 19 illustrates a hardware implementation of the L3 subsystem 59,according to some embodiments of the present invention. The control andPID/PWM computation circuitry 191 for the white point control subsystem(L3) 59 monitors and controls the behavior of each color channel controlloop 170 in the color channel intensity control subsystem (L2) 47. Inthese embodiments, the computation circuitry 191 acts as a singlecommunications channel between each of the color channel control loops170 through which command data is passed to the color channel controlloops 170 and status data is passed from the color channel control loops150.

In some of the embodiments based on FIG. 19, a light intensity sensor91, such as a photo diode, is shown to measure the white point of theimage forming system 11. In this regard, the light intensity sensor 91can be in the location represented by light-intensity sensing subsystem92 shown in FIGS. 12 and 13. Although FIG. 19 shows that the white point196 is derived from the sensor 91, however, some embodiments have thecolor channel intensity 196 generated from a summation of the colorchannel output intensities provided to the computation circuitry 191 viapower control/status bus 178. In other words, in lieu of using aseparate sensing system 92 for white point measurement, white point canbe measured from information provided by the individual laser controlloops 170 to the computation circuitry 191 via power control/status bus178. Such an arrangement corresponds to FIG. 15, and no separate sensor91 would be provided in FIG. 19.

On the other hand, the sensor 91 in FIG. 18 may be shared by the colorchannel intensity control subsystem 47, such as that shown in FIGS. 12and 13, where the sensor 91 is located downstream of the dichroiccombiner 17. In these embodiments, each color channel does not have itsown sensor 91, but instead shares a single sensor or sensing system thatmeasures individual color channel intensities as well as white point.

Returning to the detail of FIG. 19, the voltage generated by sensor 91is passed to a transimpedance amplifier 190 to generate a signal Vpower196 representative of the present intensity of the white point. Vpower196 is passed to a summation device 193, which compares Vpower 196 to aset voltage 195 and generates an error voltage 194. In this regard,Vpower 196 can correspond to the white point 303 in FIG. 14, the setvoltage 195 can correspond to the predetermined white point 305 in FIG.14, and the error voltage 194 can correspond to the difference 307 inFIG. 14. If the absolute value of the error voltage 194 is greater thana predetermined threshold amount (e.g., threshold amount 309 in FIG.14), as determined by the control and PID/PWM computation circuitry 191,one or more of the control loops 170 are instructed by the computationcircuitry 191 to accordingly adjust their color channel intensities viapower control/status bus 178 (see, e.g., process states 310, 312 in FIG.14). In stereoscopic embodiments, the left/right signal 177 can be usedby the computation circuitry 191 to determine whether it is currentlymeasuring and controlling white point of a left-eye light beam or aright-eye light beam. In these instances, processes similar to those ofFIG. 8 can be used, except that white point is measured and controlledfor the left-eye light beam and right-eye light beam separately.

FIG. 20 illustrates a relative sampling frequency of each of the levelsL1, L2, L3 in the control hierarchy. In embodiments of the presentinvention, control loops L1, L2, and L3 operate at different rates, sothat they do not interfere with each other, but cooperate to maintainthe desired white point and left-eye, right-eye balance. The speed ofeach loop varies according to how quickly a response is needed in orderto maintain sufficient projection quality.

Laser control loop L1 operates at a relatively high speed to maintainthe proper power level at each laser. In one embodiment, laser controlloop L1 operates from approximately 50kHz to approximately 200 kHz.Color channel control loop L2 operates more slowly for controlling theoutput of all lasers of the same color, but well above frame refreshrates. In one embodiment, color channel control loop L2 operates fromabout 1 kHz to about 10 kHz. White point control loop L3 operates atspeeds well below frame refresh rates. In one embodiment, white pointcontrol loop L3 operates at about 1 to 2 cycles per second or slower.

FIG. 21 illustrates one particular circuit layout that can be used toimplement a particular embodiment of the present invention. Thisembodiment is a stereoscopic embodiment with L2 and L3 control loopspresent in an illumination subsystem controller 130. L1 subsystemcontrol is not specifically shown. In FIG. 21, a power distributioncircuit 110 provides source power for laser drivers in each colorchannel, shown as laser drivers 120 r, 120 g, and 120 b. In thisembodiment, each laser driver controls a bank of six, 12, 18, or 24lasers. There is a corresponding light-intensity sensor 112 r, 112 g,112 b in each color channel, shown as a photodiode. A controller 130provides synchronization and control of laser current and actuationbased on detected conditions and optionally provides a corrective signalto one or more color channels in order to achieve suitable color balanceor white point. Controller 130 responds to instructions, such asprogrammed instructions for obtaining color balance or white point andset up at initial factory calibration or instructions enteredinteractively by an operator for adjusting color balance or white point.A motor driver and signal conditioning circuit 140 provides the logiccontrol and synchronization signals needed for operation of the shutterdisk that acts as a stereo separator 134 r, 134 g, 134 b for each colorchannel.

PARTS LIST

-   10. Light projection system-   11. Image forming subsystem-   13. Projection subsystem-   15. Light output from image forming subsystem-   17. Dichroic combiner-   19. Light modulation subsystem light dump path-   21. Image path-   22. Beam dump for light modulation subsystem-   23. Light-intensity-correction system-   26. Laser-   31. Light redirecting prism-   40 r, 40 g, 40 b. Light modulation channel-   41. Coherent light generated by light source subsystem-   42. Light source subsystem-   44, 44′. Solid-state laser array-   44 a, 44 b. Bank of polarized laser arrays-   45′ 45 r, 45 g, 45 b. Illumination combiner-   46. Mirror-   47. Color channel intensity control subsystem-   49. Laser-light intensity control subsystem-   50. Lens-   51. Integrator-   52. Light guide-   53. Translucent cover-   54. Lens-   55. Integrator downstream exit surface-   56. Integrator side-   57. Left-eye light beam-   58. Right-eye light beam-   59. White point control subsystem-   60. Light modulation subsystem-   62. Polarization beamsplitter-   64. Half wave plate-   65. Shutter-   66. Shutter motor-   67. Shutter in image path-   68. Shutter removed from image path-   69. Mechanical arm-   70. Projection optics-   71. Rotating shutter-   71 a. Transmissive segment of rotating shutter-   71 b. Reflective segment of rotating shutter-   71 c. Transition region of rotating shutter-   72. Rotating shutter motor-   73. Beam dump in light source subsystem-   74. Rotating shutter control circuitry-   75. Light-   76. Light source subsystem light dump path-   80. Display surface-   91. Light intensity sensor-   92. Light-intensity sensing subsystem-   93. Individual laser light-intensity sensor-   94. Laser driver-   100. Method-   102, 104, 106, 108, 110, 112. Method states-   103. Color channel intensity-   105. Predetermined color channel intensity-   107. Difference-   109. Threshold amount-   110. Power distribution circuit-   112 r, 112 g, 112 b. Sensor-   120 r, 120 g, 120 b. Laser driver-   130. Controller-   134 r, 134 g, 134 b. Stereo separator-   140. Motor driver and signal conditioning circuit-   150. Laser control loops-   151. Control and PID/PWM computation circuitry-   152. Current source-   153. Amplifier-   154. Summation device-   155. Laser diode-   156. Photo diode-   157. Set voltage-   158. Control signal-   159. Voltage output-   160. Error voltage-   161. Left/Right Signal-   162. Power control/status bus-   170. Color channel control loop-   171. Control and PID/PWM computation circuitry-   172. Array of lasers-   176. Vpower-   177. Left/Right signal-   178. Power control/status bus-   180. Transimpedance amplifier-   191. Control and PID/PWM computation circuitry-   200. Method-   201. Left-eye light beam color channel intensity-   202, 204, 206, 208, 210, 212. Method states-   203. Right-eye light beam color channel intensity-   207. Difference-   209. Threshold amount-   300. Method-   302, 304, 306, 308, 310, 312. Method states-   303. White point-   305. Predetermined white point-   307. Difference-   309. Threshold amount

1. A light projection system comprising: a projection subsystemconfigured at least to project an image; an image forming subsystemcomprising: a light source subsystem configured at least to generatelight, and a light modulation subsystem configured at least to cause thelight to follow either a light dump path or an image path in a mannerconsistent with image data, the light dump path not leading to theprojection subsystem, and the image path leading to the projectionsubsystem; and a light-intensity-measurement subsystem configured atleast to determine an intensity of the light and comprising alight-intensity sensor in the light dump path.
 2. The system of claim 1,wherein the image forming subsystem further comprises a plurality oflight source subsystems, each configured at least to generate a singlecolor channel of a plurality of color channels of light generated by theimage forming subsystem, wherein the image forming subsystem furthercomprises a plurality of light modulation subsystems, each associatedwith a light source subsystem and configured at least to cause light itreceives from its associated light source subsystem to follow either alight dump path or an image path in a manner consistent with the imagedata, the light dump path not leading to the projection subsystem, andthe image path leading to the projection subsystem, and wherein thelight-intensity measurement subsystem is further configured at least todetermine an intensity of each of the plurality of color channels oflight.
 3. The system of claim 2, wherein a light-dump path exists foreach of the plurality of color channels of light, and wherein thelight-intensity-measurement subsystem comprises a light-intensity sensorin each light-dump path.
 4. The system of claim 1, wherein the light isstereoscopic light comprising a left-eye light beam and a right-eyelight beam that follow a same path along the light-dump path when sodirected by the light modulation subsystem.
 5. The system of claim 4,wherein the light-intensity sensor is configured at least to measurelight intensity during a blanking period between the left-eye andright-eye light beams.
 6. A method for measuring light intensitygenerated by a light projection system, the method comprising:generating light from a light source subsystem; directing the light, bya light modulation subsystem, along either an image path or a light dumppat in a manner consistent with image data, the image path leading to aprojection subsystem configured at least to project an image, and thelight dump path not leading to the projection subsystem; and determiningan intensity of the light with in image sensor in the light dump path.7. The method of claim 6, wherein the generating generates a pluralityof color channels of light, each from one of a plurality of light sourcesubsystems, wherein the directing directs each of the color channels oflight with a light modulation subsystem along either the image path or alight dump path not leading to the projection subsystem, and wherein thedetermining determines an intensity of each of the plurality of colorchannels of light.
 8. The method of claim 7, wherein the determiningoccurs when only one of the plurality of light source subsystems aregenerating light.
 9. The method of claim 7, wherein a light-dump pathexists for each of the plurality of color channels of light, and whereinthe determining is performed with a light-intensity sensor in eachlight-dump path.
 10. The method of claim 6, wherein the light isstereoscopic light comprising a left-eye light beam and a right-eyelight beam that follow a same path along the light-dump path when sodirected by the light modulation subsystem.
 11. The method of claim 10,wherein the determining determines light intensity during a blankingperiod between the left-eye and right-eye light beams.
 12. The method ofclaim 6, wherein the determining occurs during or contemporaneously withcompletion of construction of the light projection system.
 13. Themethod of claim 6, wherein the determining occurs during orcontemporaneously with a startup procedure initiated by a powering-on orrebooting of the light projection system.
 14. The method of claim 6,wherein the determining occurs just prior to projecting a video with thelight projection system.